Acetylthio PEG derivatives, also called thioacetate PEGs, are thiol group protected functional PEGs that can be linked to various substrates. Acetythio protecting group can be easily removed under either acidic or alkaline conditions to release free thiol. Our acetythiol PEG derivatives cover a broad range of different functionalities including acetylthio PEG amine, acetylthio PEG NHS, acetylthio PEG maleimide, acetylthio PEG azide, acetylthio PEG DBCO, acetylthio PEG biotin, acetylthio PEG hydrazide and many others.